The present invention relates to a device and to a process for reducing the vibration generated on the structure of a rotary-wing aircraft, particularly a helicopter.
It is known that the main source of vibration in a helicopter is the main rotor thereof which provides lift and forward drive. Such vibration constitutes a significant problem which needs to be addressed, because this vibration causes:
cyclic stresses throughout the helicopter, leading to phenomena of fatigue and therefore having a direct influence on safety; and PA1 vibration in the cabin, which is, of course, highly prejudicial to the comfort of pilots and passengers. PA1 the frequency 1.OMEGA. represents the emergence of an imbalance in the wing structure, the source of which, may, in particular, be detachment at the leading edge of the blades, defective mast bearings, or a problem with the stiffness of the drag dampers; and PA1 the frequency 4.OMEGA. is the natural frequency of vibration of a helicopter with a four-bladed rotor. This frequency must not change for a given flight configuration. Its degradation is generally caused by a problem in the connection between the main transmission gearbox and the fuselage. PA1 2.6.OMEGA., in the case of a three- or five-blade aircraft; and PA1 2.7.OMEGA., in the case of a four-blade aircraft. PA1 a number of sensors, for example accelerometers, capable of measuring the values of measurement parameters that represent the vibration of said structure; PA1 additional adjusting means capable, as a function of the adjusting values, of adjusting adjustment parameters capable of reducing the vibrations of said structure; and PA1 a calculation unit, preferably a personal computer, capable, on the basis of the values measured by said sensors, of calculating the adjusting values of said adjusting means and of said additional adjusting means to allow the vibrations to be minimized, the adjusting values thus calculated being applied to said adjusting means and to said additional adjusting means. PA1 auxiliary masses arranged in the cuffs of the blades; PA1 pitch rods; and PA1 balance tabs. PA1 which is formed on a reduced-vibration aircraft, from a number of different adjustments and measured values of said measurement parameters each or which is the result of these different adjustments; and/or PA1 which is formed taking account of the following assumptions: PA1 M is the influence matrix; PA1 Pn is the set of adjustment values from the previous flight n; and PA1 .GAMMA.n is a matrix containing all of the measurement values of said flight n which represent the vibrations and which are the result of the adjustment values Pn.
A well-adjusted and fault-free helicopter causes the fuselage to vibrate at frequencies which are a multiple of b.OMEGA., b being the number of blades and .OMEGA. the rotational frequency of the main rotor.
The occurrence of frequencies other than harmonies of .OMEGA. indicates faults. Likewise, an increase in the intensity of said harmonics may also betray the emergence of faults of various types.
By way of example, it may be noted that, in the case of vibrations: